Subject: Re: [patch 1/2] Validate itimer timeval from userspace
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, trini@kernel.crashing.org
In-Reply-To: <20060318123102.7d8c048a.akpm@osdl.org>
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Date: Sat, 18 Mar 2006 21:38:51 +0100
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On Sat, 2006-03-18 at 12:31 -0800, Andrew Morton wrote:
> Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > On Sat, 2006-03-18 at 12:07 -0800, Andrew Morton wrote:
> > 
> > > From my reading, 2.4's sys_setitimer() will normalise the incoming timeval
> > > rather than rejecting it.  And I think 2.6.13 did that too.
> > > 
> > > It would be bad of us to change this behaviour, even if that's what the
> > > spec says we should do - because we can break existing applications.
> > > 
> > > So I think we're stuck with it - we should normalise and then accept such
> > > timevals.  And we should have a big comment explaining how we differ from
> > > the spec, and why.
> > 
> > Hmm. How do you treat a negative value ?
> > 
> 
> In the same way as earlier kernels did!
> 
> Unless, of course, those kernels did something utterly insane.  In that
> case we'd need to have a little think.

It was caught by:

timeval_to_jiffies(const struct timeval *value)
{
        unsigned long sec = value->tv_sec;
        long usec = value->tv_usec;

        if (sec >= MAX_SEC_IN_JIFFIES)
sec = MAX_SEC_IN_JIFFIES;
....
}

The conversion of long to unsigned long converted a negative value to
the maximum timeout.

It's not utterly insane, but it does not make much sense either.

Of course I can convert it that way, if we want to keep this "help
sloppy programmers aid" alive.

	tglx


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